[GlobalISel] Translate floating-point negation

Reviewers: qcolombet, javed.absar, aditya_nandakumar, dsanders, t.p.northover, ab

Reviewed By: qcolombet

Subscribers: dberris, rovka, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D30671

llvm-svn: 297171